1. Field of the Invention
The present invention relates to telescopes, telescope mounts, astronomical object locators, and drive mechanisms. More particularly, the present invention relates to an altitude/azimuth telescope mount having an integral locator using magnetic encoders and a microprocessor for facilitating location of astronomical objects, and having a drive mechanism adapted to allow for automatically or manually positioning the telescope to view the astronomical objects and for automatically repositioning or steering the telescope in order to track the astronomical objects during extended viewing, wherein components of the drive act as a clutch mechanism that effectively disengages a drive motor to avoid damage during manual movement or when encountering obstructions.
2. Description of the Prior Art
Astronomers have long desired, and telescope manufacturers have long striven to develop, an effective but easy-to-use locator system for quickly and reliably locating astronomical objects and efficiently positioning a telescope for making observations thereof. The positions of astronomical objects are based upon a spherical coordinate system involving the perpendicular axes of right ascension and declination, determination of which requires a theodolite, a clock, and an accurate knowledge of the observer's latitude and longitude. The theodolite is used to measure the object's angle above the local horizon; the object's declination is then calculated to be the angle between the Celestial Equatorial Plane (CEP) and the North Celestial Pole (NCP). An arbitrary 0° longitudinal line has been defined as a line engraved on a brass plate set in the floor of the Old Royal Observatory in Greenwich, England.
The object's right ascension requires a knowledge of the Local Sidereal Time, being based upon the moment of Local Sidereal Time the object transits the observer's zenith, or local meridian. Because the Earth makes one full turn about its polar axis every twenty-four hours, right ascension is traditionally referred to in hours, from zero to twenty-four. Note, however, that right ascension is easily converted to degrees, with one hour of right ascension equaling 15°, or 1/24 of a 360° circle. Hours are further divided into finer units of 60 arcminutes, written 60′, or 3600 arcseconds, written 60″. A good telescope under good observing conditions can resolve details as fine as 1″ on the surface of the celestial sphere.
Having successfully mastered the complex spherical coordinate system, an astronomer is not yet ready to begin observation. Because the Earth's axis of rotation moves, causing the coordinate grid to shift, an object's right ascension and declination are continually changing. Thus, an object's precise position is date dependent, with the current standard being equinox 2000.0, which means the object's right ascension and declination at the moment the year 2000 began. For example, the star Vega (Alpha Lyra) currently may be found at approximately 18 h 37 m right ascension, and approximately +38 47′ declination.
As can be appreciated, locating astronomical objects and positioning a telescope for observation can be a difficult, frustrating, and time consuming process. Furthermore, once the telescope has been repositioned to observe a second object, a large part of the process must be inefficiently and inconveniently repeated to reacquire the first object.
Large institutional telescopes can be cost effectively equipped with computer-controlled automatic locator systems requiring only that the desired object's right ascension and declination or its name or designation be entered, from which the computer can retrieve positioning data from a comprehensive database. Along with the time, date, and a knowledge of the fixed latitude and longitude of the observatory, the controlling computer can use drive motors to automatically position the telescope with positive feedback data provided by mechanical encoders.
Unfortunately, such automated systems are too expensive and cumbersome for use on small, portable telescopes. For example, common optical encoders for position determination are too expensive or use impractically complex or heavy mechanical gears or similar mechanisms. Furthermore, results of attempts to create a practical and economically feasible portable automated locator system for small telescopes have typically been sorely lacking in accuracy. Adding to the difficulty is the need to reduce weight and power consumption in order to preserve the portable nature of the telescope.
It is also desirable to be able to automatically position the telescope tube for viewing the astronomical objects and to automatically reposition or steer the telescope tube to track the astronomical objects during extended viewing. It is known in the art to use stepper motors responding to signals provided by a microprocessor to accomplish this task. The known, incremental movement of the stepper motors allows the locator system to accurately control movement of the mount and always know the telescope tube's current orientation when moved from a known starting point. Thus the locator function and movement function are interdependent. Unfortunately, any movement of the mount or telescope tube (e.g., resulting from incidental contact) that is not initiated by the microprocessor and implemented by the stepper motors can adversely affect the accuracy of the locator system. Furthermore, because the stepper motor is always physically engaged with the mount, any manual movement of the mount or telescope tube is transferred to and may strain or otherwise damage the stepper motors.
It is also known to use optical encoders for the locator function, rather than rely on the known movements of stepper motors, and thereby separate the locator function from movement function. This means that the telescope tube can be moved independent of the drive motors without affecting the locator function. Unfortunately, the drive motors remain physically engaged with the mount such that any manual movement of the mount or telescope tube is transferred to and may strain or otherwise damage the drive motors.
Due to these and other problems in the art, a need exists for an improved locator system and drive mechanism.